How is Salmonella Infection Diagnosed?
Salmonella bacteria can be detected in stool or blood cultures, and a diagnosis of salmonellosis is confirmed by culture. Specimens of blood or feces are placed in nutrient broth or on agar and incubated for 2-3 days. After that time, a trained microbiologist can recognize Salmonella bacteria, if present, by its unique characteristics.
In the stool, the laboratory is challenged to pick out Salmonella from many other similar bacteria that are normally present. Many persons submit specimens for testing after they have started antibiotics, which may make it even more difficult for a lab to grow Salmonella. So, the diagnosis of salmonellosis may be problematic and many mild cases are culture-negative.
Blood cultures are often not performed and in most cases the blood stream is not infected. Bacteremia does occur in 5 percent of adults with Salmonella gastroenteritis and can result in hematogenous spread to the heart (endocarditis), spleen, bone (osteomyelitis), and joints (reactive arthritis), although blood cultures are rarely positive.